1. Field of the Invention
The present invention relates to a photodetection device and an image display device, and for example, relates to a device for measuring illuminance of the outside through a light receiving element.
2. Description of the Related Art
Controlling an object based on a measurement of the illuminance of the outside through an illuminance meter is carried out such as, for example, for adjusting a brightness of a backlight of a liquid crystal display or turning on streetlights automatically.
Such illuminance meter uses a light receiving element to convert the intensity of received light (light intensity) into a current corresponding to the light intensity.
Since silicon (Si), which is a material for a light receiving element, has, however, a sensitivity peak in an infrared light region, in order to obtain enough sensitivity to a light in a predetermined wavelength region, for example, to a visible light or an ultraviolet light two light receiving elements having different spectral characteristics, which makes difference in the wavelength region and which cancels outputs in other regions, are combined to obtain a desired spectral characteristic.
An appropriate combination of the light receiving elements different in spectral characteristic enables realization of a spectral characteristic close to a human eye for detection of a visible light, and, detection of an ultraviolet light.
As an art for obtaining the desired spectral characteristic by combining the two light receiving elements together as described above, there is proposed a “semiconductor photodetection device” disclosed in Patent Document 1.    Patent Document 1: JP H01-207640 A
In this art, two n-type layers different in depth are formed on a p-type substrate to form two photodiodes different in spectral characteristic, and a difference in current between those photodiodes is taken to detect light in an ultraviolet region.